Astronomy quiz question: Moon rise times

Astronomy 10 Quiz 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q2.2

[3.0 points.] An observer in San Luis Obispo, CA observes that the Moon rises in the east at exactly 6:00 PM. Which one of the following choices best describes the time that the Moon will rise in the east, on the following evening?
(A) Nearly an hour earlier than 6:00 PM.
(B) Exactly 6:00 PM.
(C) Nearly an hour later than 6:00 PM.
(D) (It cannot be determined when the Moon will rise the following evening, unless the date/season is given.)
(E) (It is impossible in San Luis Obispo, CA for the Moon to rise at 6:00 PM.)

Correct answer: (C)

As seen from above, the Moon revolves counterclockwise in its approximately 29 day-orbit around the Earth, while the Earth rotates counterclockwise in approximately 24 hours. Thus the Moon will have moved approximately 1/29th further along its orbit by the time an observer on the Earth notices it is rising again, and thus the Moon will appear to rise slightly later each consecutive day.

Student responses
Section 4160
(A) : 8 students
(B) : 5 students
(C) : 16 students
(D) : 9 students
(E) : 1 student

Student responses
Section 5166
(A) : 12 students
(B) : 13 students
(C) : 28 students
(D) : 12 students
(E) : 1 student